Overload relay



Dec. 21, 1948. BE|BER|H 2,456,907

OVERLOAD RELAY Filed July 31, 1947 L0 Fluoracarbon L z'qu id Mercury w EYSSES: A INVENTOR Leo J Ber erich.

Patented Dec. 21, 1948 ovrmltoan nanny Leo J. B urberloh, Pittsburgh, Pa... alaignor to Westinghouse Electric Corporation, East Pittaburgh; Pm, a corporation oi Pennsylvania Application July 81, 1947, Serial No. 705,114

6 Claims. 1 This invention relates, generally, to overload relays, and, more particularly, to temperaturesensitive overload relays having a; liquid electrode which may be utilized as a switching member.

In the design of low-cost relays; many attempts have been made to utilize the equivalent of a mercury switch for making and breaking. en'ergized circuit connections. One of the greatest obstacles to overcome in producing such a relay has been the contamination of the mercury due to arcing caused by the interruption of circuits (Cl. zoo-422) resistance of such members to expansion or contraction. I

The top plate I; may also be made of stainless steel. After certain materials have been placed in the container, the plate I! may be welded to the bellows-like stainless steel tube ll.

and the resultant change in the characteristics of the switch. This renders it impossible to callbrate the relay properly and to make it function within predetermined limitations. Therefore, such a relay does not give adequate protection to electrical apparatus.

The object of the invention is to provide for maintaining the vapor-pressure characteristics in a mercury switch substantially constant, and to protect the mercury from contamination.

For a fuller understanding of the nature and objects of the invention, reference may be had to the following detailed description,- taken in conjunction with the accompanying drawing, in which the single figure is a view in vertical section of a relay constructed in accordance with this invention, in conjunction with a diagram showing how it may be connected in a clrcuiti' Referring now to the drawing, the relay shown generally at it comprises a metallic bellows-like member il having a bottom plate or main i2 and a top plate or member I! sealed theretgl; making a container for a purpose to be described hereinafter. a

The bellows-like member ll maybe madeof any suitable material. In making a relay for test purposes, the bellows-like member ll was made from stainless steel and was mounted on a stainless steel plate ii. The member ll may be sealed to the plate II in any suitable manner well-known in the art. In the embodiment illustrated, it is welded. I

The characteristics of the stainless steel bellows member Ii will affect the operation of the relay. Therefore, before building a relay, it is necessary to have detailed information on the stifiness of the bellows member. However, this can readily beestablished by any one skilled in the art, and a table may be prepared giving the As shown; the plate II has an'electrode II depending therefrom. This electrode H is insulated from the stainless steel plate II, as shown at i!.- Any suitable type of insulating material may be employed. In this modification of the invention, an elastomeric organosilicon oxide,v such as dimethyl silicone rubber-like composi tions, is employed to give a tight seal as welt as. to insulate the electrode l4.

' Before the plate It is welded to the bellows-- like member li, a .quantity of mercury II is poured into the bottom of the container. The amount'of mercury employed will depend uponconditions to be met. In this instance, the amount of mercury must be great enough for the end of the electrode H to be sufliciently immersed to make good electrical contact.

In order to protect the mercury from contamination during the operation of the relay. a layer of liquid fluorocarbon I! is provided. Since specific gravity of liquid fiuorocarbonsismuch less than that of mercury, it floats asillustrate'd. The amount of fluorocarbon floated on the marcury will be selected to meet the conditions to which the relay will be subjected. if?" In operating a relay having a layer of fluoro carbon floating on the mercury, it was discovered that the fluorocarbon did not readily decompose.

when subjected to arcing, and when it did decompose, it did not produce materials which contamina'ted the mercury. v

It has been found that completely fluorinated cyclic hydrocarbons with or without completely fluorinated side chains, and the completely fluorinated straight chain or aliphatic fluorocarbons may be utilized singly or in admixtures with one another with success for protecting mercury from contamination.

Examples of the completely fluorinated cyclic hydrocarbons are such as perfluoro-methyl-cyclohexane, C1Fi4, periiuoro lj3-dimethyl-cyclohexane, CaFia, perfluoro 1,3,5-trimethyl-cyclohex- Examples of completely fluorinated straight chain or aliphatic hydrocarbon liquids 3 that may be used are periiuoro-heptane, 01F and perfluoro-octane, ClFu.

The structure oi these completely fluorinated cyclic hydrocarbons is as follows:

The structure of the completely fluoridated straight chain hydrocarbons which may be utilized is given below:

iFn

It has been found that these liquid fluorocarbons are very stable with the result that the relay retains substantially constant vapor-pressure characteristics. In other words, when the relay having fluorocarbon liquids floating on the mercury is operated a number of times, it continues to give substantially the same curve of vapor pressures with change in temperature. There'- fore, when the stiffness characteristics of the bellows-like member II are known and the fluorocarbon is properly selected, the relay may readily be calibrated and it will not change appreciably during operation. Therefore, relays may be built to perform any predetermined operation.

In order to make the relay respond to predetermined overload conditions, a heating coil- II is disposed around the member II. This heating coil will be connected in some predetermined circult relation with the apparatus to be protected. In this instance, a shunt motor shown generally at I! is connected in series-circuit relation with the coil I. As the motor i8 is overloaded, the current flowing in the heating coil II will gradually raise the temperature, increasing the vapor pressure in the container causing it to expand and withdrawing the electrode ll from the mer cury. In order to explain the complete functioning of the relay iii, a brief description of its functioning in connection with the motor will be given. v

Assuming now that the manually-operated switch 20 and the push-button switch ii are both closed, then a circuit is established which extends irom one conductor of the power line 22 through conductor 23, switch 20, the mercury i0, functioning as one 01' the members of the switch of the relay ID, the electrode II. which is the other member of the switch, conductor 26, the actuating coil 25 of the relay 28, conductor, push-button switch 2i and conductor ll, back to the other conductor of the power line 22.

The relay 26 will be actuated upwardly and the contactor 29 will bridge its contacts and establish'a holding circuit through conductor N which parallels the push button ii. In this manner, the relay II is held in its raised position after the push-button switch is released.

Upon the operation oi. relay 2!, an actuating circuit ior the relay Si is established which extends from one conductor of the power line 22 through conductors 23 and 32. the actuatinl coil," of the relay 3|, conductor 34, contact member SI of the relay l8, conductor 30, back to the power line 22.

' Upon the operation oi. relay II. a motor circuit is established from the power line through conductor 38, contactor II o! the relay Ii, conductor 40, motor l9, conductor ii, the heating coil ll of the relay i0, conductor 42, contact member ll of the relay 3i and conductor 44, back to the power line.

Assuming now that the motor it becomes overloaded, the current in the motor circuit will be increased thus causing an increase oi current flow through the heating coil II. This results in raising the. temperature of the liquid fluorocarbon in the container comprising the members ii, 12 and i3. The'liquid fluorocarbon will boil increasing the vapor pressure and expanding the bellows member ii. Upon a predetermined expansion or the bellows member ii, the electrode it will be withdrawn from the mercury 16 interrupting the holding circuits of the relay 2' with the result that relay ll also is opened, interrupting the motor circuit.

As the relay cools down, the bellows member ii will contract and the electrode I will again be dipped into the mercury ii. The motor stands idle until the motor circuit is again closed by operating the push button II.

Test results have shown that when a. layer oi, for example, perfluoro 1,3-dimethyl-cyclohexane or periiuoro-heptane was floated on the mercury i8, and the relay operated five hundred times by a control voltage of 440 volts with the switch members it and I8 interrupting a current flow of one-tenth oi an ampere, no contamination of the mercury resulted. The vapor-pressure characteristics of the relay did not change.

It is pointed out that the boiling point of periluoro 1.3-dimethyl-cyclohexaneis 101 C. at 760 mm. mercury, while the boiling point of pertluoro-heptane is 82 C. at 760 mm. mercury. Therefore, in designing the relay, in order to get a predetermined operation, it becomes necessary to take these boiling temperatures into account, using either fluorocarbon alone or mixtures thereof.

In some instances. after long operation of the relay with a layer of these liquid fluorocarbons floating on the mercury, small quantities of unsaturated aliphatic fluorocarbons. such as Cal. and CLF! were produced. These products do not contaminate mercury. Further, since only small quantities of CzF4 and 041': are produced. the vapor-pressure characteristics of the relay remain substantially constant with temperature and the relay continues to operate in response to substantially the same predetermined load conditions on the motor.

It has been found in operating with relays having a layer of non-fluorinated hydrocarbon liquids floating on the mercury that the arcing caused by the separation of the switch members I4 and i8, readily decomposed the hydrocarbons and caused a considerable amount of fouling of the mercury. The result of the breaking down of the hydrocarbon is that the relay begins to operate at lower and lower temperatures. Thereiore, I

tively,

relays containing non-fluorinated hydrocarbons will not function an appreciable number of times in accordance with the calibrations.

Since numerous changes may be made in the above-described structures and diilerent embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a switch, in combination, a container capable of expanding and contracting in response to changes in internal pressure, mercury in the container to be used as one of the electrodes of the switch, a second electrode disposed in the container to move into and out of the mercury as the container contracts and expands, respecwith changes in internal pressure to perform switching operations, and a quantity of a completely fluorinated hydrocarbon liquid floating on the mercury to maintain substantially constant vapor-pressure characteristics in the container and to protect the mercury from contamination during the operation of the switch to make and break circuits carrying electric current.

2. In a switching device, in combination, a container capable of expanding and contracting in response to changes in internal pressure, mercury in the container, the mercury serving as one electrodeof the switch, a second'electrode disposed in but insulated from the container to move into and out of contact with the mercury as the container contracts and expands in response to changes in internal pressure. and a quantit of liquid perfluoro 1,3-'dimethyl-cyclohexane floating on the mercury to maintain substantially constant vapor-pressure characteristics in the container and to protect the mercury from contamination during the operation of the switching device to make and break circuits carrying electric current.

3. In a switching device, in combination, a metallic bellows-like container capable of expanding and contracting in response to changes in internal pressure, mercury in the container, the mercury being disposed to function as one electrode of the switching device, a second electrode disposed'in the container and insulated from it, the second electrode moving with the container as it expands and contracts with changes in internal pressure to break and make contact with the mercury, a quantity of perfluoroheptane floating on the mercury to maintain substantially constant vapor-pressure characteristics in the container and to protect the mercury from contamination during operation of the switching device to make and break circuits in which electric current is flowing.

4. In a relay provided with a switching device. in combination, a metallic bellows container having predetermined resistance to expansion by internal pressure, mercury in the container constituting one electrode of the switching device, a second electrode disposed in the top of the container and insulated therefrom to move with the container as it expands and contracts to break and make contact with the mercury, a quantity of fluorocarbon floating on the mercury, the fluorocarbon comprising a mixture of perfluoro 1,3-dimethyl-cyclohexane and perfluoro-heptane the fluorocarbon floating on'the mercury serving to maintain substantially constant vapor-pressure characteristics in the container and to protect the mercury from contamination during operation of the switch to make and break circuits in which electric current is flowing.

5. In a relay provided with switching members, in combination, a metallic bellows container having a predetermined resistance to expansion by internal pressure but responsive to internal pressures, mercury in the container, the mercury serving as one of the switching members of the relay, a second electrode disposed in and insulated from the container to move into and out 01 contact with the mercury as the bellows container contracts and expands in response to internal pressure, and a quantity of a liquid fluorocarbon consisting of at least one selected from the group consisting of perfluoro 1,3-dimethyl-cyclohexane, perfluoro-heptane, perfluoro methyl cyclohexane, perfluoro 1,3,5-trimethyl-cyclohexane and perfluoro-octane floating on the mercury, the liquid fluorocarbon serving to maintain substantially constant vapor-pressure characteristics in the container and to protect the mercury from contamination during operation of the switch members to make and break circuits carrying electric current.

6. In a relay provided with a plurality oi! switch members, in combination, a bellows container having a predetermined resistance to expansion in response to internal pressure, mercury in the container constituting one of the switch memhere, an electrode disposed in the container and insulated therefrom constituting the other switch member, the electrode being disposed to move as the container expands and contracts to break and make contact with the mercury, a quantity of liquid fluorocarbon floating on the mercury to maintain substantially constant vapor-pressure characteristics in the container and to protect the mercury from contamination during operation of the switch members to make and break circuits carrying electric current, and a heater disposed around the container, the heater serving to regulate the temperature of the container, the mercury and fluorocarbon in accordance with the operating conditions.

LEO J. BERBERICH.

No references cited. 

